MADRID (Reuters) - Spain said on Thursday border police had fired rubber bullets in an attempt to turn back around 200 migrants who tried to cross the frontier between Morocco and Spain's north African enclave Ceuta on February 6.

At least 11 migrants from the group drowned in the Mediterranean trying to swim around a man-made breakwater that separates Moroccan and Spanish waters, a Spanish official said on Thursday.

Every year thousands of Africans try to reach Europe via Spain's two north African enclaves, Ceuta and Melilla, either by swimming along the coast or climbing the triple walls lined with razor wire that mark the border with Morocco.

Migrants who live rough in the mountains on the Moroccan side, waiting for an opportunity to rush the frontier, told Spanish media the police fired rubber bullets at them and sprayed them with tear gas as they tried to swim to land.

Interior Minister Jorge Fernandez told a parliamentary commission on Thursday that rubber bullets had been fired at a distance of at least 25 meters from the migrants while they were in the water. He did not mention use of tear gas.

The shots were never intended to hit migrants, he said, but were used as a deterrent. The actions were appropriate given the aggressive behavior of the migrants, the minister said.

Spanish police posted video footage online of migrants throwing stones at the border fence. The footage did not show the moment when the migrants went into the sea to start trying to swim around to Spanish land.

Hundreds protested in central Madrid on Wednesday against the treatment of illegal migrants in Spain, bearing placards reading slogans such as: "Ceuta: the shame of Europe" and "South looted, North closed".

The pressure on Ceuta and Melilla has increased as more migrants try to enter via a land frontier rather than by crossing the sea in rickety vessels, because border control at sea has increased.

Around 3,000 illegal migrants entered Spain in the first half of last year, official data showed, double the figure for the same period in 2012.

Interior Minister Fernandez said on Thursday the breakwater separating Spanish and Moroccan waters would be lengthened during to deter migrants trying to swim to Spanish territory.